Wetting is a property of a liquid/solid interface governed by adhesive forces between the liquid and solid and cohesive forces in the liquid. Adhesive forces between the liquid and solid cause the liquid to spread across the solid surface. Cohesive forces in the liquid cause the liquid to minimize contact with the solid surface. The wetting of a solid surface by a liquid is important in many industrial processes where a liquid interacts with a solid surface. Electroplating (a cathodic process), including electroplating in integrated circuit manufacturing, is one such industrial process. Wetting is also important in anodic processes, including electroetching and electropolishing.
For example, in integrated circuit manufacturing, a conductive material, such as copper, is often deposited by electroplating onto a seed layer of metal deposited onto the wafer surface by a physical vapor deposition (PVD) or a chemical vapor deposition (CVD) method. Electroplating is a method of choice for depositing metal into the vias and trenches of the wafer during damascene and dual damascene processing.
Damascene processing is a method for forming interconnections on integrated circuits (ICs). It is especially suitable for manufacturing integrated circuits, which employ copper as a conductive material. Damascene processing involves formation of inlaid metal lines in trenches and vias formed in a dielectric layer (inter-metal dielectric). In a typical damascene process, a pattern of trenches and vias is etched in the dielectric layer of a semiconductor wafer substrate. Typically, a thin layer of an adherent metal diffusion-barrier film such as tantalum, tantalum nitride, or a TaN/Ta bilayer is then deposited onto the wafer surface by a PVD method, followed by deposition of an electroplate-able metal seed layer (e.g., copper, nickel, cobalt, ruthenium, etc.) on top of the diffusion-barrier layer. The trenches and vias are then electrofilled with copper, and the surface of the wafer is planarized.